Semiconductor devices are widely used in various types of electronic products, consumer products, printed circuit cards, and the like. In an integrated circuit, a number of active semiconductor devices are formed on a chip of silicon and interconnected in place by leads to form a complete circuit. The size and cost of the semiconductor devices are important features in many of these applications. Any reduction in the cost of producing the package or reduction in the size or thickness of the package can provide a significant commercial advantage.
Ball grid array semiconductor packages are well known in the electronics industry. Currently available prior types include the Plastic Ball Grid Array (PGBA), the Ceramic Ball Grid Array (CBGA), and the Tape Ball Grid Array (TBGA). A BGA package typically comprises a substrate, such as a printed circuit board, with a series of metal traces on the top side. This series of metal traces is connected to a second series of metal traces on the bottom side of the substrate through a series of wire channels located around the periphery of the substrate. A semiconductor die, having a plurality of bond pads, each associated with an input or output of the semiconductor die, is mounted to the top side of the substrate. The bond pads are connected to the series of metal traces on the top side of the substrate by wire bonds. Typically, the semiconductor die and wire bonds are encapsulated with a molding compound. The second series of metal traces located on the bottom side of the substrate each terminate with a contact pad where a conductive solder ball is attached. The conductive solder balls are arranged in an array pattern, and are connected to the next level assembly or a printed wiring board in the final application.
Alternatively, the substrate may be provided with a series of metal traces on only the bottom side, and the semiconductor die is attached to the bottom of the substrate. The bond pads of the semiconductor die are attached to the series of metal traces on the bottom side of the substrate. The series of metal traces located on the bottom side of the substrate terminate with a contact pad where a conductive solder ball is attached. The conductive solder balls are arranged in an array pattern, and are connected to the next level assembly or a printed wiring board in the final application.
FIG. 1A illustrates a cross-sectional view of a typical prior art perimeter BGA integrated circuit package 10. BGA package 10 comprises a substrate 11 having top conductive traces 12 formed on an upper surface of substrate 11. Substrate 11 typically is formed from an organic epoxy-glass resin based material, such as bismaleimide-triazin (BT) resin or FR-4 board. The thickness of substrate 11 is generally on the order of 0.35 mm. Bottom conductive traces 13 are formed on a lower surface of substrate 11 and are electrically connected to top conductive traces 12 through vias or plated through-holes 14. Vias 14 extend from the upper surface of substrate 11 to the lower surface. Vias 14 contain a conductive material such as copper. Top conductive traces 12 terminate with bond posts or pads 21. Bottom conductive traces 13 terminate with ball or terminal pads 16. Top conductive traces 12, bottom conductive traces 13, ball pads 16, and bond posts 21 comprise an electrically conductive material such as copper or copper plated with gold. Not all top conductive traces 12, bottom conductive traces 13, and vias 14 are shown to avoid overcrowding of the drawing.
BGA package 10 further comprises a semiconductor element or semiconductor die 18 attached to a die attach pad 23 on the upper surface of substrate 11. Semiconductor die 18 is attached to die attach pad 23 using an epoxy. Semiconductor die 18 has a plurality of bonding or bond pads 22 formed on an upper surface. Each of the plurality of bond pads 22 is electrically connected to top conductive traces 12 with a wire bond 19. Typically, semiconductor die 18, wire bonds 19, and a portion of substrate 11 are covered by an encapsulating enclosure 24, such as an epoxy enclosure.
Conductive solder balls 26 are each attached to a ball pad 16. Conductive solder balls 26 are metallurgically wetted to ball pads 16 during a reflow process. The inner-most conductive solder balls 26 are typically underneath or adjacent to semiconductor die 18. Conductive solder balls 26 are later connected to a next level of assembly or printed circuit board 28 using a standard reflow process. Conductive solder balls 26 connect to contact pads 29 to form solder joints 25. After the mounting process, solder joints 25 take a flattened spherical shape defined by solder volume and wetting areas. The number and arrangement of conductive solder balls 26 on the lower surface of substrate 11 depends on circuit requirements including input/output (I/O), power and ground connections.
FIG. 1B illustrates a cross-sectional view of another typical prior art perimeter BGA integrated circuit package 30. BGA package 30 comprises a substrate 31 and a support or base substrate 32 attached to substrate 31. Substrate 31 and support substrate 32 typically are formed from an organic epoxy-glass resin based material, such as bismaleimide-triazin (BT) resin or FR-4 board. The thickness of substrate 31 and support substrate 32 is generally on the order of 0.35 mm each. Substrate 31 has an opening or aperture 33, which forms a cavity with support substrate 32 as the lower cavity surface. The dimensions (length and width) of support substrate 32 are greater than the dimensions of opening 33 and less than the dimensions of substrate 31. Substrate 31 has top conductive traces 34 formed on the upper surface, and bottom conductive traces 35 formed on the lower surface electrically connected to top conductive traces 34 through vias or plated through holes 36. Top conductive traces 34 terminate at one end with a bond post or pad 38. Bottom conductive traces 35 terminate with a conductive ball pad or contact 39. A plurality of conductive solder balls or contacts 40 are each coupled to a conductive ball pad 39.
BGA package 30 also contains a semiconductor element or semiconductor die 48 attached to a die attach pad 43 on the upper surface of support substrate 32. Support substrate 32 and opening 33 provide a cavity for semiconductor die 48, which minimizes the effect of die thickness on the overall package height. Bond pads 42 are electrically connected to top conductive traces 34 with a wire bond 49. Typically, semiconductor die 48, wire bonds 49 and a portion of substrate 31 are covered by an encapsulating enclosure 50, such as an epoxy enclosure. Conductive solder balls 40 are later connected to a next level of assembly or a printed circuit board 52 using a standard reflow process.
BGA packages 10, 30 have several disadvantages, including a high profile. Height 17 of BGA package 10 is typically on the order of 2.4 mm, while height 54 of BGA package 30 is typically on the order of 0.9 to 1.46 mm. It is often desirable to minimize the thickness of a packaged semiconductor device since they are widely used in various types of electronic products, portable consumer products, telephones, pagers, automobiles, integrated circuit cards, and the like, in order to make the final products as thin as possible. Thus, there exists a need in the electronics industry for a BGA package that has a very low profile.
Another disadvantage of BGA packages 10, 30 is the cost of production. The use of substantial amounts of substrate in the manufacturing of BGA packages increases the overall cost of production. Thus, there exists a need in the electronics industry for a BGA package that is cost effective.
The present invention has been designed to address the needs of the electronics industry and to overcome some of the limitations associated with a low cost, low profile BGA package.